Anterior lumbar interbody fusion (ALIF) is a type of spinal fusion that utilizes an anterior (front—through the abdominal region) approach to fuse the lumbar spine bones together. The intervertebral disc is removed and replaced with a bone (or metal) spacer, in this case using an anterior approach. The anterior technique is often favored when multiple spinal levels are being fused and multiple discs need to be removed. ALIF may be performed in conjunction with or without a posterior decompression (laminectomy) and/or instrumentation (use of metal screws/rods). The anterior approach is also ideal when only one spinal level is fused and a posterior decompression and/or instrumentation are not required. Although the anterior lumbar approach involves retracting (moving out of the way, temporarily) large blood vessels (aorta, vena cava) and the intestines, there is a wide exposure of the intervertebral disc without refraction of the spinal nerves and neurologic structures (and therefore, a decreased risk of neurologic injury).
ALIF is commonly performed for a variety of painful spinal conditions, such as spondylolisthesis and degenerative disc disease, among others.
The ALIF approach is advantageous in that, unlike the PLIF and posterolateral gutter approaches, both the back muscles and nerves remain undisturbed.
Another advantage is that placing the bone graft in the front of the spine places it in compression, and bone in compression tends to fuse better.
Lastly, a much larger implant can be inserted through an anterior approach, and this provides for better initial stability of the fusion construct.
However, the ALIF procedure also involves resection of the anterior longitudinal ligament, which can destabilize the implanted cage.
Therefore, surgeons often combine ALIF with a posterior approach (anterior/posterior fusions) because of the need to provide more rigid fixation than an anterior approach alone currently provides. Additionally, stabilization and fixation devices have been added to a standard interbody fusion spacer to stabilize and fix the spacer in place.
The lateral approach (LIF) provides an alternate route to the spine that disturbs fewer structures and tissues. This, in combination with small incisions, means much less discomfort for the patient and fewer risks of complications. With a lateral interbody fusion, the surgeon approaches the back through a small incision in the side of the body, using special tools and techniques. There are a number of other names for the same technique, including DLIF® (Direct Lateral Interbody Fusion), XLIF® (eXtreme Lateral Interbody Fusion), and transpsoas interbody fusion.
In most cases, patients who are candidates for this surgery are those who would have needed an incision in the abdomen in order for the surgeon to reach the area of concern. Approaching the spine through the abdomen means the surgeon must get around large blood vessels, nerves, muscles, and organs that are in the way. This can prolong recovery following surgery and, in rare cases, can cause complications such as nerve or blood vessel damage.
Many existing interbody fusion spacer systems require multiple actions on the part of the surgeon with respect to cage insertion, and fixation of the cage to the vertebral bodies.
For example, the INDEPENDENCE® Spacer System (Globus Medical, Inc.) integrates a stabilization plate and a PEEK interbody spacer into a preassembled system. INDEPENDENCE® also incorporates a smooth screw blocking mechanism, minimizing disruption to the anatomy surrounding the surgical site and may lessen the long term impact from surgery. However, this system requires multiple actions by a surgeon to insert and fix it in place.
Additionally the use of a screw fixation system has a number of disadvantages. Screw fixation systems can require the use of a drill or an awl to prepare a hole in the vertebrae. Some screw systems require two different length screwdrivers to insert the screw or an initial driver to insert the screw most of the way into the vertebrae and then a torque driver to do the final tightening.
Screw fixation devices require a specific angle of insertion that requires a larger soft tissue exposure/corridor than necessary to insert the cage itself. Sometimes these angles require undue pressure on the surrounding soft tissues which could place abdominal viscera and blood vessels at risk. These fixed angles required to insert the screws can limit the ability to insert the fixation devices at the L5-S1 disc where the symphysis pubis may inhibit access.
Additionally, the fixed angles for screw insertion and limited soft tissue exposure can place excess pressure on the insertion tool and cause the screw to be inserted inappropriately and possibly strip the screw at the bone-screw interface or the screw-anterior plate interface. This may occur if the device screw uses a separate machine thread to lock the screw to the cage.
While overcoming some of the limitations associated with fixed-angle screw insertion some vertebral fixation systems utilize variable angle screw insertion, however these systems may not provide rigid fixation to the plate/cage and vertebrae. This may allow micro motion and increase the risk of failed fusion.
Screw systems, fixed or variable angle, provide little surface area contact within the vertebra to adequately resist the forces of flexion, extension, rotation, and translation/shear. A fixation system that effectively neutralizes these forces is necessary for rigid fixation. Rigid fixation eliminates the need for supplemental external immobilization devices (braces) and allows early patient mobilization and return to more normal activity.
Instrumentation and specialized tools for insertion of an intervertebral implant is yet another design parameter to consider when designing a spacer. Spinal fusion procedures can present several challenges because of the small clearances around the spacer when it is being inserted into position. For instance, the instrumentation used may securely grip the implant on opposing sides or surfaces. In U.S. Pat. No. 6,520,993 to James, et al., for example, the superior and inferior surfaces have one or more regions in which no gripping teeth are present. These protrusion-free zones enable the implant to be grasped and manipulated by elongate rectangular blades. However, the clearance required to insert the spacer must be higher than the spacer itself to accommodate the required instrumentation. For this reason, distraction of the treated area typically is greater than the implant itself.
Similarly, when the gripping tools used to manipulate and insert the implant on the sides of the spacer, additional clearance typically is needed to accommodate the added width of the insertion tool blades. Such increases in height or width of the profile of the spacer, when in communication with instrumentation, means that additional space is needed in order to insert the spacer. In some circumstances, providing for this additional clearance space can be difficult to achieve.
Thus, despite known devices that promote fusion of a treated area of the spine, there remains a need for improved fixation devices for use in interbody fusions, such as ALIF and anterior cervical discectomy and fusion.
Therefore it is an object of the invention to provide improved fixation devices and kits for interbody cages.
It is a further object of the invention to provide improved methods for achieving vertebral interbody fusions, in the lumbar or cervical spine.